1. Field of the Invention
The present invention relates to freewing aircraft. More particularly, the present invention relates to a system and method for controlling a roll rate of a torsionally-disconnected freewing aircraft.
2. Background Information
Some conventional aircraft employ wings that are free to rotate about a spanwise axis, commonly called “freewings.” Freewings are described in, for example, U.S. Reissue Pat. No. RE36,487 to Wainfain, U.S. Pat. No. 5,340,057 to Schmittle, and U.S. Pat. No. 5,395,073 to Rutan et al. The use of freewings has numerous advantages over more conventional designs. A common feature of freewing designs is the use of a tube connecting the left wing to the right wing. The tube generally serves as the pivot axis. The tube must have significant torsional stiffness to keep the two wings at the same angle relative to the body.
There have been attempts at modifying the design by eliminating the tube. Such a modification has the advantage of reducing the weight and also allowing better use of the fuselage volume. However, such modifications have been discarded as unworkable due to significant stability problems. For example, in one early attempt at uncoupled freewing design, an aircraft that was built with such uncoupled wings crashed on its first takeoff attempt. The stability problems result from the fact that torsionally disconnected freewings will cause divergent behavior of the aircraft, both to external disturbances and also to minor misalignments of the aircraft itself. The problem is so severe that misalignments that are insignificant on conventional aircraft can result in uncontrolled rolling at many revolutions per second with the torsionally-disconnected freewing.
Therefore, there is a need for a control system for torsionally disconnected freewings that can make the use of such freewings safe and practical.